It is well known to use machine tools to cut pieces of various required shapes from larger base or stock materials.
In some cases, the pieces are cut from large (e.g., twenty feet long or longer), flat materials, such as mill plates, made of thick and heavy metal. That size makes such plates difficult to handle, and further can require a large footprint for the machine tool in a facility to provide the space needed for handling. Still further, given the complexity and size of the machine tools required to cut such materials, machine tools which have often heretofore been used in such applications provide a tool which will move in one axis of the plane of the plate (the Y-axis), in which case the mill plate itself is moved in a perpendicular axis (the X-axis).
Mill plates such as mentioned above have generally rectangular shapes with generally flat sides or edges. However, the generally flat edges are typically formed with tolerances which can result in some curvature to the “flat” edges.
Machining of such mill plates typically has been accomplished by moving the mill plate while it is being machined moved with one of its “flat” edges oriented in the one (X-axis) direction and maintained in that orientation by pressing the plate edge against one or more guides oriented in the direction of plate movement (the X-axis). However, particularly where high precision is required for the cut piece, mill plate tolerances resulting in some curvature in the edge of the large mill plate can result in undesirable curvature also in the cut piece, as illustrated in FIGS. 1a-1e and FIGS. 2a-2e, which illustrate prior art methods of cutting of a rectangular piece from a mill plate 20. (For illustration purposes, the curvature of the mill plate edges is greatly exaggerated in the Figures.).
In the prior art method illustrated in FIGS. 1a-1e, a mill plate 20 is supported on an entry conveyor 24 having a plurality of datum rollers 28 pivotable about horizontal axes aligned in a horizontal plane, whereby the mill plate 20 will generally move in the horizontal direction perpendicular to the axes of the datum rollers 28.
A suitable cutting tool 30 is supported by a machine tool (not shown in FIGS. 1a-1e) for selective lateral movement across the width of the mill plate 20 (i.e., in a vertical direction in FIGS. 1a-1e).
Adjacent the area of the cutting tool 30 are a plurality of vertical datum rollers (i.e., fixed guide rollers) 34 (pivotable about vertical axes) arranged in a vertical plane substantially perpendicular to the horizontal plane/axes of the entry conveyor rollers 28. The vertical datum rollers 34 define abase position for the side of the mill plate 20 in the area of the cutting tool 30.
On the conveyor side opposite the vertical datum rollers 34 is a pusher 40 having a roller 44 (rotatable about a vertical axis) which is biased (e.g., by a piston 46) to engaging the other side or edge 48 of the mill plate 20. The pusher 40 pushes the mill plate 20 into engagement with the vertical datum rollers 34 on the opposite side of the conveyor 24. The mill plate 20 is thus essentially oriented so that the longitudinal direction of the mill plate 20 is considered to be the direction of the edge 50 of the mill plate 20 located at the vertical datum rollers 34.
Cutting of a rectangular cut piece 60 (see FIG. 1e) according to this prior art method is illustrated by the sequence of views in FIGS. 1a-1e. The mill plate 20 is first positioned so that the cutting tool 30 is positioned over one corner of the piece to be cut (FIG. 1a). The mill plate 20 is then moved horizontally by the conveyor 24 in the direction of arrow 62 (FIG. 1b), with the cutting tool 30 cutting one side 60a of the piece 60 during that movement. During that movement, the mill plate 20 is positioned by the pusher 40 pushing one mill plate edge 48 to keep the other mill plate edge 50 in contact with the vertical datum rollers 34 (aligned with the cutting tool 30) to cut one side 60a of the piece 60.
When the next corner of the piece 60 is reached, the conveyor 24 stops and holds the mill plate 20 in position while the cutting tool 30 is moved laterally across the mill plate 20 (in the direction of arrow 64, FIG. 1c) to cut a second side 60b of the piece 60.
The conveyor 24 then moves the mill plate 20 horizontally in a reverse direction (arrow 66, FIG. 1d), with the cutting tool 30 cutting a third side 60c of the piece 60 during that movement. During that movement, the mill plate 20 is positioned by the pusher 40 pushing one mill plate edge 48 to keep the other mill plate edge 50 in contact with the vertical datum rollers 34 (aligned with the cutting tool 30) to cut one side 60a of the piece 60.
Finally, when the fourth corner of the rectangular piece 60 is reached, the conveyor 24 again stops and holds the mill plate 20 in position while the cutting tool 30 is moved laterally across the mill plate 20 (in the direction of arrow 68, FIG. 1e) to cut the fourth side 60d of the piece 60.
It should be appreciated that two of the sides 60a and 60c will be essentially of the same orientation/shape as the longitudinally aligned edge 50 of the mill plate 20. Thus, if the edge 50 is not precisely linear (e.g., due to tolerances or damage), then the sides 60a and 60c will be similarly and undesirably cut in a non-linear fashion.
FIGS. 2a-2e illustrate a second prior art method of cutting large mill plates 20, wherein elements identical to those illustrated in FIGS. 1a-1e are given identical reference numerals and corresponding but different elements are given the same reference numerals with prime (“′”) added (e.g., vertical datum rollers 34′).
With this second prior art method, the mill plate 20 is oriented during movement by having edge 50 pressed toward vertical datum rollers 34′ which are positioned over a longer distance (e.g., along the entire length of the conveyor 20′) than described above in connection with FIGS. 1a-1e. However, typically the entry conveyor 24′ ends substantially in the area of the cutting tool 30, so that when the mill plate 20 is moved forward through the machine tool (as in FIG. 2b), the forward edge may extend beyond the vertical datum rollers 34′. As a result, with this second method, when cutting a mill plate 20 having a concave edge 50 such as in the illustrated example, the longitudinal orientation of the mill plate 20 will be established by the back corner 20a of the mill plate 20 and the last (forward) vertical datum roller 34′a. It should thus be appreciated that the mill plate 20 will not only move forward when cutting side 60a′ (FIG. 2b) and backward when cutting side 60c′ (FIG. 2d), but it will also slightly twist (due to the pusher 40 pushing the mill plate 20 laterally during forward and backward motion when the front corner of the mill plate 20 is beyond the last vertical datum roller 34′a).
It should be appreciated that if the edge 50 is not precisely linear (e.g., due to tolerances or damage), two of the sides 60a′ and 60c′ of the cut piece 60′ (which in the example is intended to be rectangular) will be not be linear due to the twisting of the mill plate 20 during cutting of those sides with the second prior art method as well.
The present invention is intended to overcome one or more of these problems.